Aqueous dispersions of particulate polymer or emulsified liquid pre-polymers for use as paints, sealants, caulks, adhesives or other coatings are well-known, widely-used articles of commerce. The effectiveness of the dispersion in forming a film after the polymer dispersion has been deposited upon a surface depends upon the glass transition temperature of the dispersed polymer and the temperature at which the film is allowed to dry. See, for example, Conn et al., U.S. Pat. No. 2,795,564 and Emmons et al., U.S. Pat. No. 4,131,580.
Coalescent aids have been used in such aqueous dispersions to soften, i.e., plasticize, the particulate polymers and facilitate the formation of a continuous film with optimum film properties once the water has evaporated. In addition to increasing the ease of film formation, the coalescent aid also promotes subsequent improvements in film properties by coalescing the particulate polymers and liquid pre-polymers and forming an integral film at ambient temperatures. Without the coalescent aid, the films may crack and fail to adhere to the substrate surface when dry.
Coalescent aids are particularly helpful in assisting the formation of particulate polymer films possessing a high glass transition temperature, that is, the temperature which defines how easily the particles of the polymer diffuse at the temperature at which the film-forming composition is applied. The presence of coalescent aids in a particulate polymer film having a high glass transition temperature allows optimum film formation at ambient temperatures.
Various alcohol esters and ether alcohols have been proposed for use as coalescent aids. For example, in U.S. Pat. No. 4,131,580 Emmons et al. disclose water-based coating compositions based on vinyl addition polymers of monoethylenically unsaturated monomers which comprise dicyclopentenyl acrylate and/or dicyclopentenyl methacrylate as a coalescent aid. In U.S. Pat. No. 4,141,868, Emmons et al. suggest certain ester-ether compounds be used instead.
Two of the more widely used coalescent aids are ethylene glycol monobutyl ether (EB, Union Carbide) and 2,2,4-trimethyl-1,3 pentanediol monobutyrate (TEXANOL®, Eastman Kodak). While EB and TEXANOL® are useful in facilitating film formation of particulate polymer coatings with high glass transition temperatures and are even useful in facilitating film formation of particulate polymer coatings with low glass transition temperatures if they are being applied at a temperature that is lower than ambient temperature, they are relatively volatile and, as a result, are currently classified as VOCs (volatile organic compounds).